The objectives are to investigate the mechanisms whereby the gastrointestinal hormones cholecystokinin, secretin, gastrin, and glucagon produce their mesenteric vascular effects, and to determine the relationship between mesenteric blood flow and intestinal secretion and absorption. Using anesthetized animals, the role of vasoactive intermediary substances, eg. amines, nucleotides, etc. in the vascular response to the hormones will be investigated by measuring their direct release into the blood in response to the hormones, and by comparing their effects to those produced with the hormones on intestinal blood flow, oxygen consumption, and tension responses in isolated vascular smooth muscle. Additionally, the role of a local intestinal nervous reflex-possibly employing 5-hydroxytryptamine as a neurotransmitter-- will be studied regarding the hormonal vascular mechanism. Using radioactive microspheres, the effects of the gastrointestinal hormones on intestinal mucosasubmucosa blood flow will be determined to evaluate whether induced changes at this level provide a functional basis for the processes of secretion and absorption. Secretory responses will be studied using intraluminal intestine perfusion and collection techniques to determine volume, protein, and electrolyte outputs while intestinal blood flow is monitored. Intestinal absorption will be studied using isotopic and autoradiographic techniques.